Ontology Evaluation

Ontologies are a pillar of the emerging Semantic Web. They capture background knowledge by providing relevant terms and the formal relations between them, so that they can be used in a machine-processable way, and thus enable automatic aggregation and the proactive use and serendipitous reuse of distributed data sources. Ontologies on the Semantic Web will come from a vast variety of different sources, spanning institutions and persons aiming for different goals and quality criteria. Ontology evaluation is the task of measuring the quality of an ontology. It enables us to answer the following main question: How to assess the quality of an ontology for the Web? Ontology evaluation is essential for a wide adoption of ontologies, both in the Semantic Web and in other semantically enabled technologies. We regard the three following scenarios as relevant for ontology evaluation: • Mistakes and omissions in ontologies can lead to the inability of applications to achieve the full potential of exchanged data. Good ontologies lead directly to a higher degree of reuse of data and a better cooperation over the boundaries of applications and domains. • People constructing an ontology need a way to evaluate their results and possibly to guide the construction process and any refinement steps. This will make the ontology engineers feel more confident about their results, and thus encourage them to share their results with the community and reuse the work of others for their own purposes. • Local changes in collaborative ontology engineering may effect the work of others. Ontology evaluation technologies allow to automatically check if constraints and requirements are fulfilled, in order to automatically reveal plausibility problems, and thus to decrease maintenance costs of such ontologies dramatically. In this thesis a theoretical framework and several methods breathing life into the framework are presented. The application to the above scenarios is explored, and the theoretical foundations are thoroughly grounded in the practical usage of the emerging Semantic Web. We implemented and evaluated a number of the methods. The results of these evaluations are presented, indicating the usefulness of the overall framework.